Anode and base assembly for electrolytic cells

ABSTRACT

AN ANODE AND CELL BASE ASSEMBLY IS PROVIDED WHICH FEATURES THE USE OF DEMENSIONALLY STABLE ANODES. IT IS CHARACTERIZED IN HAVING A CELL BASE WHICH SERVES AS A RIGID SUPPORT FOR THE ANODES, AS A CONDUCTOR FOR DISTRIBUTING CURRENT TO THE ANODES AND AS A RIGID SUPPORT FOR THE CELL CAN. FURTHERMORE A SHEET OF ELECTRICALLY NONDUCTIVE MATERIAL COVERS THE ENTIRE CELL BASE AND SERVES TO INSULATE THE CONTACT BETWEEN THE CELL CAN AND THE CELL BASE   AND ALSO PROVIDES A HYDRAULIC SEAL TO PREVENT LEAKAGE OF ELECTROLYTE.

Doc. 26, 1972 LQF'TFIELD ET AL 3,707,454

ANODE AND BASE ASSEMBLY FOR ELECTROLYTIC CELLS Filed June 28, 1971 ,2Sheets-Shoot '1 i i l l I l I I I 29 I V IIIIIIII V I"'-";IIIIIII'A"!4L'|IIIIIIIII RICHARD E. LOFTFIELD HENRY W LAUB ATTORNEY26, 1972 n- ET AL 3,707,454

ANODE AND BASE ASSEMBLY FOR ELECTROLYTIC CELLS 2 Shanta-Shoat 2 FiledJune 28, 1971 Fig. 4

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. INVENTORS RICHARD E. LOFTFIELD HENRY W LAUB ATTORNEY United StatesPatent O US. Cl. 204-242 5 Claims ABSTRACT OF THE DISCLOSURE An anodeand cell base assembly is provided which features the use ofdimensionally stable anodes. It is characterized in having a cell basewhich serves as a rigid support for the anodes, as a conductor fordistributing current to the anodes and as a rigid support for the cellcan. Furthermore a sheet of electrically nonductive material covers theentire cell base and serves to insulate the contact between the cell canand the cell base and also provides a hydraulic seal to prevent leakageof electrolyte.

REFERENCE TO A CO-PENDING APPLICATION This is a continuation-in-part ofour co-pending U.S. Ser. No. 763,121 filed Sept. 27, 1968, now US.Patent No. 3,591,483.

BACKGROUND OF THE INVENTION Our Ser. No. 763,121 describes thecombination of a metal base, an insulating sheet and dimensionallystable anodes for use in a diaphragm cell, the remaining components ofwhich are essentially conventional. It has been found on furtherinvestigation that much of the teaching regarding use of such acombination in a diaphragm cell, applies as well to cells of the samegeneral configuration, with regard to the cell can in which a diaphragmis not present, e.g., a chlorate or hypochlorite cell.

Many of the problems described in the previous application with regardto the diaphragm cell electrolysis of alkali metal halide solutionsemploying graphite anodes, have also plagued the producers of oxyhalogencompounds since the apparatus employed is often similar, only thediaphragm being absent.

STATEMENT OF THE INVENTION Therefore it is an object of the presentinvention to provide an anode and cell base assembly, useful with cellcans conventionally employed in the production of oxyhalogens by theelectrolysis of alkali metal halide solutions.

This and further objects of the present invention will become apparentto those skilled in the art from the specification and claims whichfollow.

There has now been found, in a cell for the electrolysis of alkali metalhalide solutions of the type comprising an anode and cell base assemblyand employing a cell can, the improvement in the anode and cell baseassembly which comprises:

(a) A conducting and supporting cell base means having holes disposedtherein for the receipt of anode risers;

(b) A single sheet of at least one electrically non-conductive materialcovering the entire cell base, having holes disposed thereincorresponding to the holes in the cell base and serving to providecompressible seals between the anodes and the cell base and between thecell can and the cell base and,

Patented Dec. 26, 1972 (c) Dimensionally stable anodes, said anodescomprising an electrically-conductive surface, a material supportingsaid conductive surface and an anode riser having a flange on the lowerportion thereof and extending past said flange and through the cellbase.

Such an assembly has extremely low resistance to the passage of currentfrom bus bar to anode; may be assembled and disassembled rapidly andwith good dimensional accuracy; may be operated at higher currentdensities, yields greater cell power, alkali metal halide conversion andcurrent efiiciencies; allows fabrication of taller cells therebyconserving floor space, and Provides a relatively constant voltage overthe entire life of the cell, all as opposed to cathodically similarelectrolytic cells employing graphite anodes.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified end view of a typicalanode and cell base assembly employing the improved construction andadvantages of the present invention.

FIG. 2 is a simplified side view of a portion of a typical assemblyaccording to the present invention.

FIG. 3 is a simplified view of a method of connecting an anode riser andcell base according to the invention and also shows the directconnection of a connecting condoctor to the aode riser used when thecell base is of a less conductive metal and does not serve as both asupport and conducting means.

FIG. 4-6 represent anode configurations and designs which may be usedaccording to the practice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It should be understood thatthe novelty of the instant invention does not reside in the design orconfiguration of the cell can. By cell can it is intended to refer tothe portions of the cell other than the anode and cell base assembly,that is, the side walls, end walls and cover together with the cathodemembers which are attached to at least one of the walls or the cover andextend into the chamber defined by the walls and cover. Any of the cellcans currently in use are acceptable and may be adapted to the presentinvention provided that they may be deployed over the alternating arrayof anodes presented by the anode and cell base assembly of theinvention. Typically, these cell cans employ electrically conductiveside and end walls with cathode sheets, generally of iron or steel,traversing the chamber formed from sidewall to sidewall and inelectrical connection therewith. It is understood that, in the absenceof a diaphragm, there are no separate anolyte and catholyte compartmentsand therefore the products of electrolysis, e.g., chlorine and caustic,react within and/ or without the cell to produce the desired oxyhalogencompounds, e.g., sodium chlorate.

In essence the instant invention resides in (1) the cell base means, (2)the non-conducting sheet covering the cell base and (3) thedimensionally stalble anode and riser.

The conducting and supporting cel'l base means may be selected from oneof two basic designs. In the first and preferred embodiment a unitconstruction will serve both as a supporting and electrical conductingmeans. In this embodiment the base will generally be constructed of amaterial selected from the group consisting of copper and aluminum,although steel and the like may be used in some instances, and willconsist merely in a flat unit construction having disposed therein anumber of holes through which the anode risers will extend. The outsideelectrical source (bus bar) will be connected directly to the cell baseand current will fiow through the base to the anode risers. In a secondembodiment the cell base means will be constructed of a somewhat lessconductive material, such as iron or steel, which will serve mainly as asupport for the cell. This less conductive material will again be in theform of a unit construction having holes disposed therein through whichthe anode risers will extend. However, in this instance a series ofconnecting conductors to which the individual anode risers may beconnected, thereby providing direct distribution of the current to theanodes, completes the cell base means.

According to the simplified construction of the present invention thereis provided over the entire surface of the cell base a thin,electrically nonconductive, sheet of material, preferably rubber.Titanium, which is generally nonconductive under conditions of celloperation may also be used if means for obtaining a compressible seal,such as O-rings and gaskets, are provided. This nonconductive sheet ofmaterial will also have holes disposed therein corresponding to theholes in the cell base for insertion therethrough of the anode risers.Generally, the holes will be slightly larger than the holes in the cellbase in order to provide metal (riser) to metal (cell base) contact andafford good dimensional alignment. In the event that titaniumconstitutes the nonconductive layer, however, the hole need only be ofthe same dimension as the holes in the base. This nonconductive materialis intended to serve as a seal to prevent the leakage of brine aroundthe anode riser into the holes through which the anode risers extend.The nonconductive sheet of material also serves as a gasket to preventleakage of brine between the cell base and the cell can and insulatesthe positively charged cell base from the negative cell can. In theinstance where the nonconductive sheet is composed of rubber or a likematerial, the area which is in contact with the cell can may be providedwith a ribbed surface which will act as a gasket to prevent leakage ofbrine from the cell. Alternately a ridge may be provided on the rubbersurface which will compress somewhat under weight to provide a sealwhich is made more effective by the application of a small amount ofchemically inert putty around the interior circumference of the cell. Inthe event that the nonconductive sheet is of a more rigid material suchas titanium, it will be necessary to provide a gasket of rubber or thelike material which will aid in preventing leakage of brine from thecell. Other designs will be obvious to those skilled in the art.

The dimensionally stable anodes which are useful in the practice of thepresent invention comprise an electrically-conductive surface, amaterial supporting said electrically-conductive surface and an anoderiser in contact with the material which supports theelectricallyconductive surface, said riser having a flange on the lowerportion thereof and extending below said flange for such a distance asto project through the cell base. The electrically-conductive surface ofthe dimensionally stable anodes may be composed of any material whichhas a sufliciently low chlorine overvoltage and which is chemicallyinert to the electrolyte as well as resistant to the corrosiveconditions of the cell. Typically this electricallyconductive surfacewill be composed of platinum group metals, alloys of platinum groupmetals, platinum group oxides, mixtures of platinum group oxides andalloys which are mixtures of platinum group metal oxides with platinumgroup metals. Also contemplated and especially preferred at this timeare electrically-conductive surfaces which are mixtures of valve metaloxides with platinum group metals and platinum group metal oxides. Forexample, anode surfaces which are especially preferred at this timeinclude platinum metal, platinum-palladium metal alloy platinum-iridiumalloy, platinum oxide, ruthenium oxide, mixtures of platinum andruthenium oxides, titanium oxide-ruthenium oxide alloys, titaniumoxide-iridium-ruthenium oxide alloys, and the like. Again the inventionis not dependent upon the particular nature of theelectrically-conductive surface involved, it

being only important that it have an appropriately low chlorineovervoltage and good resistance to cell conditions.

The material which supports the electrically-conductive surfacegenerally comprises a valve metal or an alloy thereof. By valve metal itis intended to refer to the filmforming metals such as titanium,tantalum, zirconium, niobium and the like. This material will preferablybe in the form of a continuous sheet of metal but it may be perforatedor foraminous in order to provide circulation of the anolyte. Thesevalve metals have in common the property of being nonconductorsthemselves under the conditions of cell operation (an oxide of the valvemetal quickly forms on the surface thereof thus preventing passage ofcurrent), but being able to conduct current when anelectrically-conductive material is in contact with a portion of thesurface thereof.

The material which supports the electrically-conductive surface is incontact with, generally by welding, the anode riser. This riser servesto dispose the anode in the proper manner within the cell and to conveyelectrical current to the anode surface. The riser is preferablyconstructed, at least on the outer portions thereof, of a valve metalsuch as titanium or tantalum. As an alternative to using a riserconsisting of a solid valve metal, it is possible to use a copper,sodium or aluminum-cored riser having a layer of a valve metal on theoutside. This is preferable both due to the lower cost of the copper,sodium or aluminum and because such metals are inherently betterconductors of electricity than are the valve metals. This riser isdesigned to have a flange on the lower portion thereof which flangeserves to contact the nonconductive sheet of material covering the cellbase and provide a compressible seal therewith, thereby preventingleakage of the anolyte through the cell base. The riser then has afurther extension which allows it to project through the cell base. Thisextension may be an integral portion of the riser or it may consist, forexample, of an electrically-conductive metal stud, such as copper, whichstud screws into the bottom of the anode riser and extends therefrom. Inthe case of the construction where the cell base is, for example, ofaluminum and therefore serves as both the support and conductor, theextension of the anode riser is fastened at the bottom of the cell baseby means of a nut, which nut serves to draw the flange on the anoderiser into intimate contact with the sheet of nonconductive materialthereby effecting a hydraulic seal. In the instance where the base isconstructed of a less conductive material such as steel, a nut will alsobe provided which comes in contact with the bottom of the cell base andprovides the force for forming the compressible seal, however, the riserwill further extend through a connecting conductor and on the bottom ofthis conductor another nut will be provided for tightening the riser tosaid conductor and providing electrical contact.

Referring now to the drawings in which corresponding elements in thedifferent figures have the same number, FIG. 1 is an end view of atypical anode and cell base assembly according to the present invention,the conventional cell can not shown. In this figure the cell base 1 isconstructed of a material such as aluminum or copper and serves as boththe supporting means for the cell and as the conductor. The power supply7 is attached directly to this base, for example, by means of a nut 9and bolt 11. The nonconductive sheet 3 covers essentially all of thecell base 1 and is constructed of an elastic material such as rubber.The protrusions 5 and 6 on nonconductive sheet 3 perform separatefunctions. Protrusion 5 serves as a gasket on which the cell can rest. Asmall amount of putty 29 lines the inside of the protrusion to insurethat no leakage occurs. Protrusion 6 serves as a deflector to preventbrine or water from getting between the non-conductive sheet 3 and thecell base 1. The anode 19 is connected, for example by welding, to theanode riser 13, which riser extends through the nonconductive sheet andcell base and is fastened on the bottom of the cell base by means of anut 17. The riser is also provided with a flange 15 which upontightening the nut 17, forms a hydraulic seal with the nonconductivesheet of material 3 thereby preventing leakage of anolyte through thecell base. While it is indicated in FIG. 1 that two anodes extend acrossthe width of the cell, this number is not critical and may be changed asconditions warrant.

FIG. 2 is a partial side view along the length of an anode and cell baseassembly. This figure shows essentially the same features as in FIG. 1,however, there is also indicated on the anode 19 the electricallyconductive surface 21, greatly exaggerated for illustration, in factbeing on the order of from 1 to 5 microns in thickness.

FIG. 3 is a cross-section of an anode and cell base assembly similar tothat in FIGS. 1 and 2 with the difference that in this case the base 1is constructed of a less conductive material. Therefore it is oftendesirable to use a series of connecting conductors 23 to supply thecurrent to the individual anodes. Thus, the power supply 7 is connectedto the conductors 23 by means of nut 9 and bolt 11 and nuts 27 serve toprovide contact of the conductors 23 with the extension of the anoderiser 13, which in this case is a copper stud 25. In this figure it isalso shown that the holes in the nonconductive sheet 3 are somewhatlarger than the holes in the cell base 1 thereby providing a certainamount of metal to metal contact between the anode riser 13 and the cellbase 1. Not only is this desirable in that it provides an additionalpath for current flow in a construction such as in FIGS. 1 and 2, but itis also important to good anode alignment. The copper stud 25 is seatedin the anode riser 13 by means of threads and provides an eflicientcurrent conducting means without the necessity for intricate machiningof the anode riser. This copper stud 25, however, is not required andthe riser itself may extend through the cell base 1 to make contact withthe current conducting means.

A cell embodying the present invention has a number of advantages ascompared to the prior art cells of this type employing graphite anodesin the typical complicated and cumbersome base structure in which theanode blades are inserted in a copper grid which is then covered with abonding layer of an electrically conductive material, such as moltenlead, followed by a layer of asphalt, to prevent leakage, an finally byconcrete. Beside the obvious advantages that will accure from thesimplier construction of the present invention, a number of significantoperating advantages are obtained. In the first place, a cell employingthe instant anode and cell base assembly will exhibit a constant voltageover the total life of the cell, whereas cells of the prior artemploying graphite anodes require a gradual increase in voltage in orderto maintain a constant current density owing to the increase inanode-cathode gap occasioned by anode attrition. Furthermore, it isobserved that, whereas the increase in voltage required to off-set theincreased resistance going from the bus bar in a conventional cell tothe graphite anodes is on the order of 200 milivolts, in a cellemploying the anode and cell base assembly of the present invention,only an additional 25 to 100 millivolts will be required. Owing to itsstability and the lessened resistance to passage of current through theassembly, it has been found that, whereas the prior art was limited tooperation within the range of from 0.5-1.0 ampere per sq. inch, it isnow possible to operate at good efficiency using current densities onthe order of from 1-6 a.s.i. or higher. In other words, the productionof the cell may be increased sixfold. Obviously then it is possible toobtain a much higher capacity using the same amount of floor space.Again owing to the lessened resistance of the anode and base assembly, ataller cell is possible, resulting in a capacity advantage. Because ofthe fact that the present invention does not employ materials which tendto deteriorate upon operation, such as asphalt or concrete, the purityof the products of electrolysis is significantly great- Theconfiguration and design of the dimensionally stable anodes to be usedin accordance with the practice of the present invention involve such anumber of variables that in general it may be said that essentially alldimensionally stable anodes are operable. As is stated hereinabove,foraminous valve metals as well as valve metals in sheet form may beused to support the electrically-conductive surface. FIGS. 4-6 representpreferred embodiments of anode design and configuration according to thepractice of the present invention. These figures are illustrative only,however, and variations in configuration and design which will occur tothose skilled in the art are also useful. FIGS. 4-6 represent top viewsof the anodes 19 which are attached to the risers 13, typically bywelding. In FIG. 4 it will be seen that the anode 19 is formed from acontinuous sheet of valve metal which is bent at 33 in the form of a Zwhich serves to close the anode structure and provide structuralsupport. FIG. 5 illustrates the use of two U-shaped valve metal members31 which extend from the top to the bottom of the anode 19. The members31 are attached to the anode 19, again by welding. FIG. 6 represents asimilar anode employing only one member 31. It may also be desirable toprovide the anodes with braces in order to prevent mechanical distortionof the surfaces of the anode. This may be accomplished in any number ofways, for example, by inserting three pairs of U-shaped braces (notshown) between the two anode faces with the base of the U attached tothe anode riser.

Illustrative of the invention, a typical cell base is constructed from acontinuous sheet of aluminum 84.9 inches by 43.0 inches and 1.5 inchesthick. Into this cell base there are drilled 46 holes having a diameterof 0.77 inch into which are inserted 46 anodes comprising 23 rows. Theseanodes are constructed of platinum-coated titanium sheets mounted oncopper-cored titanium risers and have a configuration corresponding tothat shown in FIG. 6. The distance from the top of the anode to the cellbase is 27.5 inches and the diameter of the riser is 1.25 inches (riserplus flange diameter, 2 inches). Into the bottom of the anode riserthere is screwed, for a distance of 2 inches, a copper stud having adiameter of 0.75 inch and extending through the cell base and 2 inchesbeyond. The nonconductive material which covers the base consists of acontinuous sheet of neoprene rubber having-46 holes thereincorresponding to the holes in the cell as :but having a diameter of 1.25inches. The sheet is fitted with ridges, one of which serves as a gasketand the other as a deflector to prevent seepage of liquids between thenonconductive sheet and the cell base.

While the invention has been described with reference to certainspecific embodiments thereof, it is understood that it is not to be solimited since alterations and changes may be made therein which arewithin the full and intended scope of the appended claims.

We claim:

1. In an electrolytic cell for the electrolysis of alkali metal halidesolutions of the type comprising an anode and cell base assembly and acell can, the improvement in the anode and cell base assembly whichcomprises:

(a) a conducting and supporting cell base means having holes disposedtherein for receipt of anode risers;

(b) an electrically nonconductive sheet covering the entire cell base,having holes disposed therein corresponding to the holes in the cellbase and serving to provide a compressible seal between the anodes andthe cell base and between the cell can and the cell base and,

(c) dimensionally stable anodes, said anodes comprising anelectrically-conductive surface, a material sup porting said conductivesurface and an anode riser having a flange on the lower portion thereofand extending past said flange and through the cell base.

2. A cell as in claim 1 wherein the cell base means comprises a unitconstruction of a highly conductive metal selected from the groupconsisting of copper and aluminum and provides both a mechanicalsupporting means and electrical conducting means.

3. A cell as in claim 1 wherein the cell base means comprises, incombination, a mechanically supporting unit construction of a lessconductive metal which is iron or steel and a number of connectingconductors of a highly conductive metal to provide current to theindividual anodes.

4. In an electrolytic cell for the electrolysis of alkali metal halidesolutions of the type comprising an anode and cell base assembly and acell can, the improvement in the anode and cell base assembly whichcomprises:

(a) a unit cell base construction of aluminum having holes disposedtherein for the receipt of anode risers;

(b) a single sheet of rubber covering the entire cell base and havingholes disposed therein corresponding to and slightly larger than theholes in the cell base and,

(c) in dimensionally stable anodes which comprise an electricallyconductive surface, a valve metal supporting said surface and an anoderiser having a flange on the lower portion thereof, said riser extendingpast said flange through the holes in the cell base cover and cell baseand being in electrical contact with said cell base.

5. In an electrolytic cell for the electrolysis of alkali metal halidesolutions of the type comprising an anode and cell base assembly and acell can, the improvement in the anode and cell base assembly whichcomprises:

(a) an iron cell base of unit construction having holes disposed thereinfor the receipt of anode risers;

(b) a single sheet of rubber covering the cell base and having holesdisposed therein corresponding to and slightly larger than the holes inthe cell base;

(c) dimensionally stable anodes comprising an electrically-conductivesurface, a valve metal supporting the conductive surface and an anoderiser having a flange on the lower portion thereof, said riser extendingpast said flange through and beyond the cell base and,

(d) a series of connecting conductors in electrical contact with theextensions of the anode risers.

References Cited UNITED STATES PATENTS 3,385,779 5/ 1968 Nishiba et a1204-275 X 3,497,446 2/ 1970 Clapper et a1. 204-242 3,558,465 1/ 1971Colvin et a1. 204-242 X I OHN H. MACK, Primary Examiner D. R. VALENTINE,Assistant Examiner US. Cl. X.R.

